Dual mode operation continuously variable transmission having creeper low and reverse gears

ABSTRACT

An automatic transmission for an automotive vehicle includes a continually variable drive mechanism having one sheave assembly fixed to an intermediate shaft and the input sheave assembly supported on an input shaft, gearset driveably connected to the input shaft and an output shaft, a fixed ratio drive mechanism in the form of a chain drive providing a torque delivery path between the intermediate shaft and the carrier of the gearset, a transfer clutch for connecting and releasing the first sheave of the variable drive mechanism and input shaft, a low brake, and a reverse brake.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to automatic transmissions for automotivevehicles. More particularly it pertains to continuously variabletransmissions having gearing for producing low gear and reverseoperation.

2. Description of the Prior Art

A conventional multiple speed transmission has a number of spaced speedratio changes produced by selectively holding and releasing componentsof a planetary gear set. An infinitely variable transmission thatemploys two variable diameter pulleys, and a drive belt engaging thepulleys provides a continuously variable speed ratio over a broad rangeof engine speeds.

A bladed hydrokinetic torque converter located in the drive path betweenan engine and the planetary gearing provides additional torquemultiplication for accelerating a motor vehicle from rest. A stalltorque ratio of about 2.5:1 may be realized using a torque converter.

A continuously variable transmission combining a fixed drive unit,variable drive unit, and torque converter is described in UK Patentapplication GB-2180020, assigned to the assignee of the presentinvention. After the torque converter reaches its coupling phase, whenthe ratio of the hydrokinetic unit is 1:1, the drive ratio for thepowertrain is reduced to 8:1 from approximately 20:1 when the fixeddrive ratio is 2:1 and the final drive and axle system ratio is 4:1. Atthat time the variable ratio drive is activated. Upon furtheracceleration of the vehicle, the overall transmission ratio may becontrolled from 8:1 down to 2:1.

U.S. Pat. Nos. 4,856,369, 4,836,049 and 3,203,277 describe continuallyvariable transmissions that employ a variable drive mechanism and afixed drive mechanism in combination with a torque converter andplanetary gearing.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a transmission able toaccelerate a motor vehicle from rest through a speed reduction drivethat bypasses a belt driven variable ratio drive mechanism so that therelatively large starting torque is carried by robust mechanicalcomponents and not by torque limited components, such as a drive belt.

It is another object of this invention that the transmission produce acontinuously variable speed ratio over a range from the first gear(starting gear) ratio to the highest ratio, an overdrive ratio.

It is yet another object of the invention to provide a transmission ableto drive both front and rear wheels from two output shafts and withoutneed for a transfer case to divide output torque carried on a singleoutput shaft and to transmit torque to front and rear driveshafts.

According to the invention a continuously variable transmission for anautomotive vehicle includes an input shaft; an intermediate shaft; anoutput shaft; a variable ratio drive mechanism having an input, and anoutput driveably connected to the input and intermediate shaft, forproducing a continuously variable ratio of the speed of the input to thespeed of the output; a transfer clutch for alternately driveablyconnecting and disconnecting the input of the variable ratio drivemechanism and input shaft; a fixed ratio drive mechanism having an firstelement, and a second element driveably connected to the first elementand intermediate shaft; a first gearset including a first sun gear, afirst set of planet pinions meshing with the first sun gear, a carrierrotatably supporting the first planet pinion set and driveably connectedto the first element and output shaft, a second sun gear, a first ringgear surrounding the second sun gear, a second set of planet pinionsdriveably connected to the first set of plane pinions, rotatablysupported on the carrier and meshing with the second sun gear and firstring gear; a low brake alternately holding against rotation andreleasing the first ring gear; and a first clutch for driveablyconnecting the input shaft to the first and third sun gears, and forreleasing said connections.

Power is transmitted to front axles by a second output shaft; and asecond clutch for alternately driveably connecting and disconnecting theintermediate shaft and second output shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the kinematic arrangement for anautomatic transmission according to the present invention.

FIG. 2 is a chart showing the engaged and disengaged state of clutchesand brakes of the transmission of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, a continuously variable transmissionaccording to this invention includes an input shaft 12, rear outputshaft 14, front output shaft 15, variable ratio drive mechanism 16,fixed ratio drive mechanism 18, planetary reverse gearset 20, planetarylow gearset 22, and various clutches and brakes for controlling themechanical elements of the transmission.

Fixed ratio drive mechanism 18 driveably connects a carrier of thegearsets and a first sprocket wheel 24 to intermediate shaft 26, whichsupports a second sprocket wheel 28, sprockets 24, 28 being mutuallydriveably engaged through a chain 30. Alternatively, shaft 26 can bedriveably connected to shaft 14 through another fixed ratio gearmechanism, such as a simple layshaft arrangement including gears inplace of sprockets 24, 28 and an idler gear meshing with those gears sothat shaft 26 turns in the same direction as shaft 14. The firstsprocket 24 is rotatably supported on shaft 14; the second sprocket 28is fixed to and rotatably supported on intermediate shaft 26.

The engine crankshaft 40 is driveably connected to a hydrokinetic torqueconverter 46 that includes a bladed impeller wheel 42 arranged in atoroidal fluid flow path with a bladed turbine wheel 44, arranged to bedriven hydrodynamically by fluid exiting the impeller wheel. A bladedstator wheel 48 is located in the flow path between fluid entrance tothe impeller and the fluid exit of the turbine. A one-way clutch 50rotatably supports the stator wheel and allows it to rotate in onedirection about the axis of shaft 12. The torus of the torque converteris filled with hydraulic fluid, and the turbine wheel 44 is supportedrotatably on a turbine hub 52, which is connected driveably to inputshaft 12. A hydraulically operated bypass clutch 53 alternatelymechanically connects engine shaft 40 and input shaft 12 when clutch 54is engaged, and allows impeller 42 to drive turbine 44 hydraulicallywhen clutch 53 is disengaged. The torque converter produces torqueamplification and speed reduction until it reaches coupling speed.

Input shaft 12 is connected, preferably through torque converter 46, toa source of power, such as an internal combustion engine or electricmotor. Rear output shaft 14 is driveably connected to the drive wheelsof a motor vehicle, preferably to the rear wheels. Front output shaft 15is driveably connected to the drive wheels of a motor vehicle,preferably to the front wheels. Alternatively, output shaft 14 can beconnected to the front axles, and output shaft 15 can be connected tothe rear axles.

Variable ratio drive mechanism 16 includes a first sheave assembly,which includes pulleys 54, 56 supported rotatably on input shaft 12, anda second sheave assembly, which includes pulleys 58, 60 fixed to andsupported rotatably on intermediate shaft 26. The axial position of oneof the first pair of pulleys 54, 56 is fixed on the input shaft, theother pulley of the pair is moveable axially along the shaft, preferablyin response to hydraulic pressure applied to an actuating device, sothat the radial position of the drive belt 62 moves in accordance withthe axial position of the axially displaceable pulley due to theinclined surfaces of the pulley faces that engage driveably the lateralsurfaces of the drive belt 62. Similarly, one of the pulleys 58, 60 onshaft 26 is fixed in its axial position, and the other pulley is axiallydisplaceable so that the inclined inner faces of the pulleys arecontinually engaged at a variable radial position with lateral surfacesof drive belt 62. Movement of the displaceable pulleys is mutuallycoordinated so that they maintain driving contact with the belt. In thisway the speed ratio produced by mechanism 16 is continuously variable.

Gearset 22 includes sun gears 64, 66 supported for rotation about theaxis of input shaft 12, a ring gear 68 coaxial with and surrounding sungear 64, sets of mutually connected planet pinions 70, 72, pinions 72meshing with sun gear 64 and ring gear 68, pinions 70 meshing with sungear 66, and a carrier 74 rotatably supporting planet pinions 70, 72 anddriveably connected to output shaft 14 and sprocket wheel 24.

The reverse gearset 20 includes a sun gear 76 driveably connected to sungear 64, a ring gear 78 coaxial with and surrounding sun gear 76, afirst set of planet pinions 80 meshing with ring gear 78, a second setof planet pinions 82 meshing with sun gear 76 and the members of thefirst set of planet pinions 80, the carrier 74 rotatably supporting thepinions 80, 82.

The elements of the transmission according to this invention arecontrolled operatively by various clutches and brakes, preferablyhydraulically actuated friction devices, including low brake 98, reversebrake 100, transfer clutch TRF 102, and torque on demand (TOD) clutch104. These clutches may be hydraulically, mechanically or electricallyoperated. Low brake 98 alternately holds ring gear 68 against rotationand releases the sun gear to rotate freely; reverse brake 100alternately holds against rotation and releases ring gear 78; transferclutch TRF 102 alternately driveably connects and releases pulleys 54,56 and shaft 12; and torque on demand (TOD) clutch 104 alternatelydriveably connects and releases intermediate shaft 26 and output shaft15.

First or low gear is produced by moving dog clutch 84 leftward todriveably engage sun gear 64, engaging low brake 98, and releasing allthe other friction elements, except that clutch 104 is engaged whendrive to both front and rear axles is desired, as discussed below. Brake98 holds ring gear 68 fixed against rotation, and sun gear 64 is drivenby the input shaft 12. Therefore, carrier 74 and shaft 14, which isconnected driveably to the rear wheels, are underdriven in the samedirection as the direction and speed of the engine. Carrier 74 can drivethe front axle through drive mechanism 18, shaft 26, TOD clutch 104 andshaft 15. In this way four-wheel drive and/or all-wheel drive can beproduced by engaging clutch 104. TOD clutch 104 may be modulated tocontrol the magnitude of torque transmitted to shaft 15.

Creeper first gear results by moving dog clutch 84 rightward intoengagement with sun gear 66 and engaging low brake 98. These actionscause carrier 74 to be underdriven at a speed ratio greater than that oflow gear. A power off shift-on-the-fly shift between low gear andcreeper first gear can be produced.

Preferably the speed ratio produced in first gear through operation ofgear unit 22 is spaced slightly from the speed ratio at the low speedend of the continually variable range produced through operation of thevariable ratio drive 16. In this way the transition from first gear tothe lowest variable gear ratio is an upshift.

An upshift to the continuously variable range is accomplished byengaging transfer clutch 102 and disengaging the dog clutch 84 and otherfriction elements. In the CVT mode, TRF clutch 102 connects input shaft12 to a first sheave, whose pulleys 54, 56 drive the pulleys 58, 60 of asecond sheave through belt 62 at variable speed ratio that depends onthe relative diameters of the sheaves where belt 62 engages the pulleys.Shaft 26, which is driven by pulleys 58, 60, drives sprocket 28, chain30, carrier 74, output shaft 14, and the rear wheels. The TOD clutch 104can be used to driveably connect the second sheave to the front outputshaft 15, as described above.

Reverse drive is produced by engaging reverse brake 100, moving dogclutch leftward into engagement with sun gears 64 and 76, which aredriveably connected mutually, and disengaging the other frictionelements, except that TOD clutch 104 may be engaged to drive the frontwheels when desired, as explained below. These actions hold ring gear 78fixed against rotation. Since sun gear 76 is connected to input shaft12, pinions 80, 82 are driven rotatably by sun gear 70, and carrier 74,which revolves due to rotation of pinions 80 on ring gear 78, isunderdriven in the opposite direction in relation to the speed anddirection of the engine and input shaft 12. The rear wheels are drivenin this way by carrier 74 through output shaft 14. The carrier alsodrives sprocket 24, from which the front wheels are driven through thefixed ratio drive mechanism 18, TOD clutch 104 and front output shaft15.

Creeper reverse gear is obtained by moving dog clutch 84 rightward intoengagement with sun gear 66 while maintaining reverse brake 100 engaged.The torque reaction is provided at ring gear 78, and carrier 74 isunderdriven in the reverse direction relative to the speed and directionof shaft 12, at a gear ratio greater than that of reverse gear. Thetorque delivery path is the same as that described above for first gearand reverse gear.

Preferably the gear ratio produced in reverse gear is -2.385; the gearratio in creeper reverse gear is -8.695.

Preferably, the speed ratio produced in the creeper first gear is 6.252,in low gear it is 2.833, at the low speed end of the continuallyvariable range it is 2.018, at the mid-range of the CVT range where bothsheaves have the same speed it is 1.009, and at the high speed end ofthe continually variable range it is 0.525. Therefore an upshift fromcreeper first gear to low gear produces a gear ratio step of 2.206 and aupshift from low gear to the low speed end of the CVT range produces agear ratio step of 1.404. When the variator mechanism 16 operates at thelow speed end of its range, the speed of pulleys 58, 60 is 0.50 timesthat of pulleys 54, 56; at the high speed end of its range; that speedratio is 1.923. Sprockets 24 and 28 have 144 and 133 teeth,respectively.

Although the form of the invention shown and described here constitutesthe preferred embodiment of the invention, it is not intended toillustrate all possible forms of the invention. Words used here arewords of description rather than of limitation. Various changes in theform of the invention may be made without departing from the spirit andscope of the invention as disclosed.

We claim:
 1. A continuously variable transmission comprising:an inputshaft; an intermediate shaft; an output shaft; a variable ratio drivemechanism having an input, and an output driveably connected to theinput and intermediate shaft, for producing a continuously variableratio of the speed of the input to the speed of the output; a transferclutch for alternately driveably connecting and disconnecting the inputof the variable ratio drive mechanism and input shaft; a fixed ratiodrive mechanism having an first element, and a second element driveablyconnected to the first element and intermediate shaft; a first gearsetincluding a first sun gear, a first set of planet pinions meshing withthe first sun gear, a carrier rotatably supporting the first planetpinion set and driveably connected to the first element and outputshaft, a second sun gear, a first ring gear surrounding the second sungear, a second set of planet pinions driveably connected to the firstset of plane pinions, rotatably supported on the carrier and meshingwith the second sun gear and first ring gear; a low brake alternatelyholding against rotation and releasing the first ring gear; and a firstclutch for driveably connecting the input shaft to said first sun gearor said second sun gear, and for releasing said connections.
 2. Thetransmission of claim 1 further comprising:a second output shaft; and asecond clutch for alternately driveably connecting and disconnecting theintermediate shaft and second output shaft.
 3. The transmission of claim1 wherein the first clutch further includes means for driveablyconnecting the input shaft to said second gear and a third sun gear andto said second sun gear alternately, and for releasing said connections.4. The transmission of claim 1 further comprising:a torque converterhaving an impeller adapted for a driveable connection to a power source,a turbine adapted for a hydrokinetic drive connection to the impellerand driveably connected to the input shaft.
 5. The transmission of claim1, wherein the fixed ratio drive mechanism includes a first sprocketdriveably fixed to an element of the first gearset, a second sprocketdriveably fixed to the intermediate shaft, and a flexible continuouselement driveably engaging said first sprocket wheel and said secondsprocket wheel; andthe variable ratio drive includes a first sheave, asecond sheave driveably fixed to the intermediate shaft, and a flexiblecontinuous element driveably engaging the first sheave and second sheaveat steplessly variable radial positions.
 6. A continuously variabletransmission comprising:an input shaft; an intermediate shaft; an outputshaft; a variable ratio drive mechanism having an input, and an outputdriveably connected to the input and intermediate shaft, for producing acontinuously variable ratio of the speed of the input to the speed ofthe output; a transfer clutch for alternately driveably connecting anddisconnecting the input of the variable ratio drive mechanism and inputshaft; a fixed ratio drive mechanism having an first element, and asecond element driveably connected to the first element and intermediateshaft; a first gearset including a first sun gear, a first set of planetpinions meshing with the first sun gear, a carrier rotatably supportingthe first planet pinion set and driveably connected to the first elementand output shaft, a second sun gear, a first ring gear surrounding thesecond sun gear, a second set of planet pinions driveably connected tothe first set of plane pinions, rotatably supported on the carrier andmeshing with the second sun gear and first ring gear; a reverse gearsetincluding a third sun gear driveably connectable to the input shaft, asecond ring gear surrounding the third sun gear, a third set of planetpinions supported rotatably on the carrier and meshing with the thirdsun gear, and a fourth set of planet pinions supported rotatably on thecarrier and meshing with the second ring gear; a reverse brake foralternately holding against rotation and releasing the second ring gear;a low brake alternately holding against rotation and releasing the firstring gear; and a first clutch for driveably connecting the input shaftto the first or the second sun gear and for releasing said connections.7. The transmission of claim 6 further comprising:a second output shaft;and a second clutch for alternately driveably connecting anddisconnecting the intermediate shaft and the second output shaft.
 8. Thetransmission of claim 6 wherein the clutch further includes means fordriveably connecting the input shaft to the first and third sun gearsand to the second sun gear alternately, and for releasing saidconnections.
 9. The transmission of claim 6, wherein the fixed ratiodrive mechanism includes a first sprocket driveably fixed to an elementof the first gearset, a second sprocket driveably fixed to theintermediate shaft, and a flexible continuous element driveably engagingthe input sprocket wheel and output sprocket wheel; andthe variableratio drive includes a first sheave, a second sheave driveably fixed tothe intermediate shaft, and a flexible continuous element driveablyengaging the input sheave and output sheave at steplessly variableradial positions.
 10. A continuously variable transmission comprising:aninput shaft; an intermediate shaft; an output shaft; a variable ratiodrive mechanism having an input, and an output driveably connected tothe input and intermediate shaft, for producing a continuously variableratio of the speed of the input to the speed of the output; a fixedratio drive mechanism having an first element, and a second elementdriveably connected to the first element and intermediate shaft; a firstgearset driveably adapted for connection to, and release from the inputshaft, and connected to the output shaft and first element, for drivingthe output shaft at a slower speed than the speed of the input shaft; asecond gearset driveably adapted for connection to, and release from theinput shaft, and connected to the output shaft and first element, fordriving the output shaft in the opposite direction and at a slower speedthan the direction and speed of the input shaft; a transfer clutch foralternately driveably connecting and disconnecting the input of thevariable ratio drive mechanism and input shaft; and a low brakealternately holding against rotation and releasing an element of thefirst gearset, whereby the output shaft is driven at a slower speed thanthe speed of the input shaft when the low brake is engaged.
 11. Thetransmission of claim 10 wherein the first gearset includes: first sungear, a first set of planet pinions meshing with the first sun gear, acarrier rotatably supporting the first planet pinion set and driveablyconnected to the first element and output shaft, a second sun gear, afirst ring gear surrounding the second sun gear, a second set of planetpinions driveably connected to the first set of plane pinions, rotatablysupported on the carrier and meshing with the second sun gear and firstring gear.
 12. The transmission of claim 10 further comprising:a secondoutput shaft; and a second clutch for alternately driveably connectingand disconnecting the intermediate shaft and second output shaft. 13.The transmission of claim 10 further comprisinga second gearsetincluding a third sun gear driveably connectable to the input shaft, asecond ring gear surrounding the third sun gear, a third set of planetpinions supported rotatably on the carrier and meshing with the thirdsun gear, and a fourth set of planet pinions supported rotatably on thecarrier and meshing with the second ring gear; and a reverse brake foralternately holding against rotation and releasing said second ringgear, whereby the output shaft is driven at a slower speed and in theopposite direction than the speed and direction of the input shaft whenthe reverse brake is engaged.